This invention relates to testing tools for stall alarms used on aircraft.
The importance of detecting an airplane stall in advance to enable a pilot to prevent the stall has caused most or all aircraft to have stall alarms. While several types of stall alarms exist, a common type consists of a horn installed in a wing leading edge. The horn emits a sound or shriek when flight conditions are trending to a stall as detected by the creation of an atmospheric vacuum at the wing leading edge; an inherent aerodynamic feature of a stalled wing. The vacuum draws air through the horn, making a sound.
A stall horn can be rendered inoperative by a variety of failure mechanisms including a hidden blockage, but pilots rely on the horn to warn of an impending stall. Because failure of the horn can lead to an unanticipated stall and an airplane crash, the alarm should be tested prior to every flight. Preflight procedures do specify a mandatory stall horn operation check. A Cessna Aircraft Corp. publication, entitled "MODEL 152 INFORMATION MANUAL" dated 1981, states on page 4-6 ". . . 2. STALL WARNING OPENING--CHECK for blockage. To check the system, place a clean handkerchief over the vent opening and apply suction; a sound from the warning horn will confirm system operation." This procedure checks the horn by orally creating a vacuum at the horn.
The leading edge of an aircraft passes through the atmosphere at high speed during flight with the consequence that the area around the stall horn is subjected to insect impact. The horn is contaminated by insect fluids and debris, such that oral contact and suction with the area, even through a cloth, is unpleasant. Additionally, the stall horn is often located above the height of an average sized pilot such that it is out of easy reach. Many pilots do not test the stall horn for the reasons stated above.
A search of the prior art has revealed no prior art relating to a stall warning horn testing tool. The Cessna booklet teaches away from the use of any tool. A search of pilot supply shops and mail order catalogs indicates a total absence of any such tool. As an example in point, refer to the Sporty's Pilot Shop Catalog, dated August, 1992.
Consequently, it is an object of this invention to provide a stall horn testing tool which will avoid the disadvantages discussed and result in safer aviation generally.